Polymerization process utilizing dextran as a primary dispersing agent



United States Patent POLYMERI ZATION PROCESS UTILIZING DEX- TRAN AS APRllVIARY DISPERSING AGENT No Drawing. Application June 10, 1954 SerialNo. 435,935

7 Claims. (Cl. 260-923) This invention relates to the polymerization ofethylenically unsaturated materials, and more particularly relates tothe production of resins comprising polyvinyl chloride.

There are four general methods ofpolymerization employed in industry,the particular method used depending on economic considerations, as wellas the ultimate use to which the polymer is put. These four methods arebulk polymerization, solution polymerization, emulsion polymerization,and suspension polymerization.

Bulk polymerization is accomplished by subjecting a pure liquid orgaseous monomer to polymerizing conditions Although a pure polymer isobtained, diffic'ulties are encountered in bulk polymerization; Forexample, air bubbles and other imperfections often find their way intothe polymer product, thereby producing a haze in otherwise clearmaterials. Equally disadvantageous are the problems of molecular weightcontrol and dissipation of the heat of reaction, matters that becomeincreasingly difiicult as the polymerization-proceeds and the reactionmass becomes more viscous.

The disadvantages of a continuous and elaborate heat control system,which is generally necessary in bulk polymerization, are substantiallycompletely overcome by solution polymerization, wherein the monomer isdissolved in a solvent and the polymerization is carried out insolution, the polymer being separated by precipitation. The heatgenerated during the reaction is dispersed throughout the entiresolvent-solute system, thereby reducing or eliminating overheating.However, not only are costly amounts of solvent required, but also thereaction rate is relatively slow and the polymer obtained by solutionpolymerization has a relatively low average molecular weight and cannotbe completely freed of solvent.

The disadvantage encountered in the two prior methods, i. e., difficultheat control in bulk polymerization and low molecular weight products,slow reaction, and presence of solvent in solution polymerizationpolymer, are substantially overcome by polymerization in an emulsifiedphase, the so-called emulsion polymerization. This type ofpolymerization requires a number of ingredients for successfuloperation, generally including an emulsifying agent, protective colloidsand/ or buffers. While emulsion polymerization overcomes many of thedifiiculties in the aforementioned types of polymerization, thereremains the problem of obtaining a substantially pure product free fromemulsifying agents and other additives necessary to maintain theemulsion, or latex. Hence, the final product of emulsion polymerizationcontains impurities which render it unsatisfactory for a number ofimportant applications. For example, it is almost impossible to preparea material of good clarity such as is necessary for use in forming filmsand sheets. Moreover, the poor dielectric qualities of the productrender it unsatisfactory in many electrical applications, even whengreat care is exercised in washing the product.

The remaining type of polymerization is suspension polymerization,improvements in which the present invention is concerned. Suspensionpolymerization is also known as granular polymerization or pearlpolymerization, the three terms being synonymous and in contrast to theprior discussed methods of polymerization. The practice of suspensionpolymerization is now well-known to involve suspending monomer in wateror other nonsolvent and, while so suspended, efiecting polymerization.Heat and catalysts are employed as polymerization aids and thesuspension is maintained during the course of the reaction by agitationand generally by stabilizing the system with a so-called suspensionstabilizer. When the polymerization is complete, the polymer isrecovered in particle or granular form by filtration or centrifugationwithout the aid of any additional specific means. The product isthereafter washed and dried and is ready for the market.

There are many variations of the granular polymerization methodgenerally described above. These variations appear in the art because ofthe specific difiiculties that are encountered in its practice. Thesimple change from emulsion polymerization to granular polymerizationdoes not lead to problem-free operation. In fact, some of thedifiiculties found in emulsion polymerization are also experienced ingranular polymerization, notably, the production of a stock materialwhich, when processed to form products, contain what is known to the artas fisheyes. In the production of a high-quality general-purposepolyrneric material, it is perhaps misdescriptive to refer to anyparticular disadvantage as being most important. However, if any singleone is most important, it is poor colloidability, as evidenced by theformation of fisheyes. This is because of the fact that all productsformed from fisheye-producing polymeric stock are inferior in quality inseveral important functional aspects, depending upon the number and sizeof fisheyes present.

Fisheyes may be visualized as small blotches, actually having theappearance of the eyes of fish, in the final plasticized polymericproduct. They are believed to result from the failure of some of theindividual particles of the polymer stock to associate with theplasticizer. Thus, as to substance, they are merely small particles ofpolymer surrounded by relatively large seas of plasticizer. Since theplasticized material is intended to be homogeneous, fiisheyes indicatepoor homogeneity and are imperfections in the final product. Arelatively small number of fisheyes can be tolerated in the finalproduct; in fact, it ap pears impossible to eliminate them completely byany process. The seriousness of their presence in large numbers may beindicated by the following comments which refer to the undesirableeffects that they have.

Excellent transparency of polyvinyl chloride in some applications, forexample, sheets and films, is an absolute necessity, both functionallyand appearance-wise. Where such products contain a substantial number offisheyes, they are not clear and transparent; instead, they present ahazy appearance and may be degraded in clarity to the point of meretranslucency. As noted above, dielectric strength in some electricalapplications is important and where the product contains many fisheyes,it is unsuitable for these uses because of the reduced dielectricstrength. Additionally, fisheyes result in the formation of a rough,uneven surface which cannot be smoothed. Products containing fisheyesare low in structural strength; especially the tear resistance ofpolyvinyl chloride sheets is seriously impaired. Fisheyes areundesirable for still other reasons which need not be mentioned butwhich are appreciated by those skilled in the art.

Patented Oct. 21, 1958 While, as noted above, the polymeric mass that isproduced by a properly managed granular polymerization method may bequite easily and quickly washed free of impurities and is readily dried,it is extremely ditlicult to control the particle size of the granularmass that is formed, whereby such case of washing and drying isattained. From the standpoint of operating efficiency, and thus thecommercial advantage in low production cost that the granularpolymerizationprocess affords, the prob-.: lem. ofparticlefsizeis.frequentlyasserious as .the problem It will 'berecalledrfromthe foregoing paragraphs that. the.polymerizedfproducLmust.be separatedfrom. the aqueous medium. Thi's may be accomplished byusualfiltration or centrifugingmethods 'pr ovided=that theprod-f uctis'withina suitable particlejsize. range. If the par.-

ticle size is too small, .separationwill be difiicultand ex-..

tremely' slow and,- in fact, may be impossible-fin 'thepractical's'ense. I A mass .of small .particles' holds'the occluded. suspendingmedium and prevents its releasefrom thenmass. Also,- .the' particlesthemselves may .pass throgh the filter. alongwitli'the liquidl j.OriIthe'other .hand, if the particles: are too large, -or.iftheparticles.arenotofa uniform .de-.. sired size, serious obstacles areencounteredin processing the polymer to its. final product.stage.vBecause. of ,the

processing requirements for .hal'ndlihg larger particles, an.

inferior product results.

For example, in processing polyvinyl; chloride to.she'et J. form,.it 'iscustomary to admixwith it a plasticizer and.

deliver it to' a milling machine. such as the well-known rollr'nillfwhichworks" the [mixturesto homogeneity., It?

ficulty because the polymer must remain upon the mill 1 until. allparticles have been. equally'plasticized in order to .obtain ahomogeneous product.

Various attempts have been made to explain the reason for the formationof large globules or agglomerates ofthe polymer. It 'has been reportedthat during the polymerization reaction,the mass passes through asticky, tacky state which is not broken up completely inthe succeedingphase of the reaction and that violent agitation see'msonly to increasethe tendency toward agglomeratio'n. Also, it isreported that thereaction rateand the temperature in'the reaction zone is thought to beresponsiblefor the problem. .The'se possibilities need not be deniedhere' asjthey may be entirely valid assumptions when considered in thelightof the particularprocess in which they originate. However, it issuggested herein that the proper approach to solving the problem ofuni-. form particle size resides in the basic suspension system itself,and that, if the suspension systemis properly .established, a preferredparticle size can be obtained, and other conditions, such astemperature,reaction rate and agitatioh exhibit a reduced influence upon particlesize.

It'is, therefore,.a principal object of theflpresent invention toprovide an improvedi suspension system during polymerization to producea polymer having enhanced processability and uniformity.

A further object of the invention is the provision of an improvedsuspendingagent for USCLiIl suspension poly-- merization.

These and other objects and advantages will appear more fully from thefollowing description of the .invention.

The present invention broadlycornprises the suspension polymerization of.an unsaturated monomer utilizing as a suspension system .dextran eitheralone or as a primary dispersant in combination with certain secondarydispersants. Hence, as used in the specification and claims, theexpressions suspension stabilizer or suspension agent are intended toinclude both the use of dextran alone, and also its use in combinationwith one or more secondary dispersants.

Typical but not limitative of secondary dispersants for use inaccordance with the practice of the present invention are water-soluble,or water-dispersible, substances selected from the following materials:formaldehyde condensation resins, such as phenol formaldehyde, ureaformaldehyde, and melamine formaldehyde resins; non-ionic materials,including polyethylene glycol .esters, glyceryl monoesters, such asglyceryl monolauratc, glyceryl monostearate, glyceryl monooleate, andglyceryl'monoricino leate, alkyl aryl polyether alcohols, such as .alkylphenoxy polyoxyethylene ethanolsysorbitanfatty acid esters andderivatives; polyoxyethylene sorbitan fatty acid esters and derivatives,such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitanmonopalmitate, polyoxyethylene sorbitan. tristearate; polyvinyl alkylethers and their-copolymers with maleicv anhydride, as well as derivatives of .such ethers and vcopolymers; polyvinyl pyrrolidones; andglyceryl phthalic alkyd resins and derivatives.

In addition, in certain'instances, it is possible to employ as secondarydispersants such materials as gelatin, polyvinyl alcohols, methylfcellulose, .polyacrylamides, and polyacrylic acidresins...

Dextran is .a carbohydratematerialhaving.the general:. formula.

wheren is greater..than..zero.. Dextranis produced by certainbacteriafrom molasses,..beet juice, milk, or wine. Illustrative .of..suitable.commercially available.dextrans. are those obtained from.the. R.K..Laros.Co. having ap-;- proximate molecular. weightsof 18,000, 74,000,228,000, and7,400,000.

While the process buwhich, polyvinyl; chlorideresinszz. may be preparedaccording to thisinventioninvolvesthe correlation of anumbenofreaction.conditions, .the process, in the main, is.notdiflic'ult to.manage.,as.a sustained. commercial operation. ItiisInecessary. only to observe... with care the -,various' conditions.thatare described: herein whereby, :it is believed, a product isobtained whichis equal t'o, if hot-superionto, anyknown commercialpoly.vinyl chloride'product. .Th'elreaction time is not.inordi-.. natelylong., lfrequires less ;than -about-15.' hours..under preferredconditions and, fit fdes'ired, Jean be .speeded. up g. considerably.

In. ordertha't those interested inflpreparing. resinous... materials inaccordance witlilthis: invention may..do..so with -facility, it isdesired .to makespecific reference .to the several'variableswhich.'are.involved,.and, further, to call attentiontocertainiprecautions that have beenv found to contribute, at least iniasmall way, to the-overall success ofthe process.

It will be appreciated that the. conditions hereinafter referred tomaybe varied.frorn-a particular suggested optimum figureeither-because.of.the.success .of the. process does not dependuponthe.maintenance of=.the. condition with suchexactness;or.because the.alteration of a particular condition. may. be. compensated. for..by.;the... alteration of another condition. operatingconcurrently. Again,it shouldbenoted.thatspecific'conditions set forthv hereinafter relateparticularlylto the .production of poly-v vinyl chloride; therefore,.where other resinous mate-.. rials are produced, it mayebeifoundthatslightlymodified conditions are desirable;

As' to'the precautions, some. of them are Well-known. in the art andwhilethecornplete success vofthe process. is not dependent upon theobservance of. the .precautions,.. and the invention is not limited .tothe application. OfzSUCh. precautions, their observance is recommended,especially in the production of polyvinyl chloridelwhereby, in :some.cases, a better product is produced or a particulardifiiculty is reducedin its magnitude.

The suspension stabilizer content may, of course, be varied somewhat indiflierent applications. However, it is generally desirable to employthe dextran in a small but effective amount, typically within the rangefrom aproximately 0.025% to 1.0% by weight of the monomer present. Whena secondary disperant is employed, its concentration generally also maybe varied within the range of about 0.025 to 1.0% by weight of themonomer present.

The reaction temperatures herein suggested do not appear to have anysignificant efiect upon either the particle size or the number offisheyes that may result in a finally formed product. However, as iswell known, high temperature generally results in the production of apolymeric material of reduced strength. Accordingly, the temperatureshould be maintained at a level con sistent with good molecular weightand adequate speed of the reaction. For example, lauryl peroxide is anerlective catalyst in the polymerization of vinyl chloride and excellentresults are thereby obtained by operating at a temperature of about 120to 130 F. This temperature range is in most instances preferred.However, the reaction proceeds with good order at from about 105 to 160F., although about 115 to 140 F. is more suitable, since at about 105 F.the reaction is slow, and at temperatures of about 160 F. and above someundesirable fusion of particles may take place.

The invention is not restricted to any particular catalyst, since thereaction conditions suggested do not interfere with the activity of thecatalyst and no well-recognized catalyst is known which defeats the endsof the invention, it being preferred, of course, to employ a catalystsoluble in the monomer to be polymerized. Accordingly, for example,there may be employed any of the well-known catalysts, such as benzoylperoxide, lauryl peroxide, dicaproyl peroxide, acetyl benzoyl peroxide,diacetyl peroxide, p-tertiary-butyl perbenzoate, tertiary butylperlaurate, di-tertiary-butyl peroxide; organic azo compounds, such asalpha, alpha'azodiiso butyronitrile and dimethyl alpha,alpha'-azodiisobutyrate. Each catalyst will have its optimumconcentration, that is to say, a concentration sufficient to efiect asubstantially complete polymerization at a suitable reaction rate. Thereaction proceeds without diificulty or disadvantage in the presence ofany of the well-known polymerization catalysts with concentrations of0.10- 0.40% by weight of the monomer. However, catalyst concentrationsof about 0.150.30% are more suitable because of improved reaction rateand, generally, about 0.200.25% by weight of monomer is preferred. Whilethe effects of excessive catalyst concentration are not especiallynotable, it has been observed that an excess of catalyst tends toproduce a material of reduced heat stability, and one having slightlyreduced strength characteristics which are apparently due to a reductionin molecular weight. In selecting the catalyst, especially if the endproduct is to be used in electrical applications where dielectricstrength is a factor, care should be taken to select a catalyst whichwill not be detrimental in this respect and, further, it should notexert an emulsifying effect. The peroxide catalysts are preferred,lauryl peroxide being a suitable and especially effective catalyst.

The method by which the reaction is initiated may exert an influenceupon product quality. It will be understood, however, that no particularstart-up method is critical to the ends of the invention; rather, thepreferred procedure seems to serve to enhance the final result.

The reaction may be carried to 100% conversion, or substantially so, ifdesired, but may also be terminated short of completion as desired or asconvenience of plant conditions may dictate. When the reaction iscomplete to the desired extent, the polymer may be separated from theremaining monomer and reaction medium by known means.

Raw material purity and contamination are quite important, sinceimportant properties of the product may be adversely affected thereby.In particular, aldehydes, phenols, acetylinic compounds, iron and sodiumsalts,

calcium, soaps, fatty acids and the like may be in the raw material orenter the system from an outside source and precautions should be takento insure reasonable to maximum purity at all times.

Generally, it is preferred to conduct the polymerization at a pH ofabout 7.0. However, in some instances it is desirable to operate in anacid medium. Various acids may be utilized to effect the desired pHvalue, the prominent controlling factor in its selection being that itshould not impair dielectric properties. Thus, acids such as sulfuric,hydrochloric, phosphoric and acetic are suitable, phosphoric acid beingpreferred.

The water-monomer ratio in the system is not critical. This ratio mayvary from about 1.504:1. More suitable, however, due to decrease involume to be handled, is a water-monomer ratio of about 1.90-3z1, thepreferred ratio being about 1.90-2.25 :1. All of these ratios are volumeratios.

In order that those skilled in the art may better understand theinvention and a method by which the same may be carried into effect, thefollowing specific exam ples are offered:

EXAMPLE I Into a bottle reactor containing the desired amount of water,i. e, 2:1 water-monomer ratio, is introduced lauryl peroxide as apolymerization catalyst. The desired amount of dextran is then weighedinto the bottle reactor containing the catalyst and the distilled water.

The amounts of peroxide and dextran are dictated by the amount ofmonomer to be used and are indicated in Table I. The resultantwater-peroxide-suspension agent mixture is then cooled until icecrystals are observed to prevent decomposition of the peroxide. Thedesired amount of distilled vinyl chloride monomer is then added,preferably in a slight excess. The excess monomer is allowed toevaporate at room temperature, thereby purging the bottle reactor ofair. The bottle is then capped and placed in a temperature controlledpolymerizer, where it is maintained for 12 hours at a temperature ofabout 122 F. with constant agitation. At the end of this period, thebottle is removed and the polymer examined. The results of a series ofsuch runs are shown in Table I.

Table I.Vinyl chloride polymerization dextran as a suspension stabilizer[2:1 water-monomer ratio, 0.30% lauryl peroxide catalyst 15 hoursreaction at 122 F. with continuous agitation] suspending AgentConversion to Bulk Run No. Concen- Polymer, Density, tration, Percentgmslcc. Molecular Wgt. Per- Wgt. cent of Monomer EXAMPLE II FORMULATIONThe following approximate quantities of materials are provided: about33.3 gallons of deionized, deaerated '2' water, about 16.7 gallons ofpurified vinyl chloride, about 0.25% (by weight of monomer) of laurylperoxide, and about 0.30% (by weight of-monomer) ofdextran (molecularweight 74,000).

' PROCEDURE About 31 gallons of deaerated water are charged to aglass-lined jacketed reactor, the water being at room temperature. Avacuum of about 27 inches of mercury is pulled on the reactor and vinylchloride monomer introduced to the reactor to bring it back toatmospheric pres sure. The vacuum treatment is repeated and more vinylchloride monomer is introduced to the reactor. The suspension stabilizeris added and thesystem is now agitated for a period of about 30 minutesto secure good dispersion. Thecatalyst is then charged, followed bycharging of the monomer. All valves are thenclosed, the agitator startedto turn at about 25 R. P. M., and the reactor is brought toapproximately 125 F. over about the next two hours and there maintainedfor 12 hours. Cold water is then delivered to the .jacket and the systemis cooled rapidly to about room temperature. The charge is then blown toa centrifuge and there spun as dry as possible, after which it is washedwith about four displacements of water. The v mass is then again spundry, after which it is delivered to trays for final drying. It is then afinished material, ready for processing.

EXAMPLE III FORMULATION PROCEDURE The procedure described in ExampleI isfollowed in this example and a product comparable in substantially allrespects is obtained.

The polymer particles obtained in accordance with the practice of thepresent invention are characterized by highly porous structure whichenhances their ability to accept plasticizer upon further processing.Accordingly, the products formed from the polymer are entirely free ofthe disadvantages mentioned hereinbefore relating to problems that areencountered because of excessive quantities of particles that are toolarge or too small.

The polymer has excellent dry-blending qualities. For example, it may bemixed with any of the well-known plasticizers, both monomeric andpolymeric types, without any tendency to become sticky or syrupy.Examples of such plasticizers are dioctyl phthalate and the polyestersformed by condensation of polyhydric alcohols and dibasic acids, as wellas epoxidized unsaturated polyesters.

Products which are formed from granular polymeric material. produced asin the above example exhibit outstanding properties in all respects.Because of the substantial absence of large fisheyes and the very smallquantity of small fisheyes, sheets, films, and other finished productsare unusually strong. Likewise, such products are of excellent clarity.

While the invention generally has been described with particularreference to the production of polyvinyl chloride, it may be employedalso in the polymerization of other unsaturated monomers, and in .theproduction of polyvinyl chloride copolymers, especially copolymers inwhich vinyl chloride constitutes at least 85% of the mixture ofmonomeric materials.

Thus, the process of the invention is applicable to the polymerizationof other unsaturated monomeric material, such as vinyl esters ofcarboxylic acids, for example, vinyl stearate, vinyl acetate, vinylpropionate, vinyl butyrate,

vinyl benzoate; esters of unsaturated-acids, for example, methylacrylate, ethylacrylate, butyl acrylate, allyl acrylate, and thecorresponding esters of methacrylic acid; vinyl aromatic compounds, forexample, styrene, orthochlorostyrene, parachlorostyrene,2,5-dichlorostyrene, 2,4- dichlorostyrene, paraethyl styrene, divinylbenzene, vinyl naphthalene,alpha-methyl styrene; dienes, such asbutadiene, chloroprene;-amides, such as acrylic acid amide, acrylic acidanilide; nitriles, such as acrylic acid nitrile; esters ofa,B-unsaturatedcarboxylic.acids, for example, the methyLethyl, propyl,butyl, amyl, hexyl, heptyl, octyl, allyl, methallyl and phenyl esters ofmaleic, crotonic, .itaconic, fumaric acids and the like. The process ofthe-invention isalso applicable to vinyl halides broadly, e. g., 'vinylchloride-vinyl bromide, etc. The method also is applicable to processeswherein vinyl chloride is polymerized with unsaturated monomericmaterials as typified by the foregoing materials.

While there have been described various embodiments of the invention,the methods described are not intended to be understood as limiting thescope of the invention, as it -is realizedthat changes 'therewithin arepossible, and it is furtherintended that each element recited in any ofthe following claims is to be understood as referring to allequivalentelements for accomplishing substantially the same results insubstantially the same or equivalent manner, it being intended to coverthe invention broadly inwhatever form its principle may be utilized.

What is claimed is:

1. 'The process of producing high-quality polymeric material whichcomprises dispersing a polymerizable monoethylenic monomer in water withthe aid of dextran in an amount within the range from about 0.025 to1.0% by .weight of the monomer and effecting polymerization of.saidmonomerwhile so suspended.

2. The process of producing high-quality polymeric material, saidprocess comprising dispersing polymerizable monoethylenic monomericmixture containing at least by weight of vinyl chloride in water withthe-aid of up to about 1.0% of dextran based on the weight of monomericmixture and polymerizing said monomeric mixture with the aid of heat anda polymerization catalyst.

3. The process of producing high-quality polymeric material, saidprocess comprising dispersing a polymerizabl e monoethylenic monomer inwater with the aid of dextran in an amount of about 0.025% to about 1.0%by weight of the monomer as a primary dispersant, in combination withabout 0.025 to about 1.0% by weight of monomer of a secondary dispersantselected from the group consisting of formaldehyde condensation resins,polyethylene glycol esters, glyceryl monocsters, alkyl aryl polyetheralcohols, sorbitan fatty acid esters, polyoxyethylene sorbitan fattyacid esters, polyvinyl alkyl ethers, polyvinyl pyrrolidones, andglyccryl phthalic alkyd resins and polymerizing said monomer with theaid of heat and a polymerization catalyst.

4. A suspension polymerization process for producing a high-qualitypolymeric material containing at least 85% by weight ot polyvinylchloride, said process comprising dispersing a vinyl chloride-containingmonoethylenic monomericmixture and a peroxy polymerization catalyst inwater, the proportions of said monomeric mixture to water being withinthe range from about 1.5-4.0:1, with the aid of 0.025 to 1% by weight ofdextran based on the weight of said monomeric mixture and while sodispersed heating the monomeric mixture-water catalyst suspension withcontinuous agitation to a temperature within the range from to F. toefiect polymerization.

5. The process according to claim 4 wherein the polymerization catalystis a monomeric mixture-soluble peroxy compound.

10 References Cited in the file of this patent UNITED STATES PATENTS2,440,808 Neher et a1. May 4, 1948 2,473,929 Wilson June 21, 19492,666,042 Nozaki Jan. 12, 1954 OTHER REFERENCES Advances in CarbohydrateChem, vol. 4, pub. by Academic Press Inc., New York, N. Y., 1949, p.333.

Dextran-A Selected Bibliography, pub. by Northern Regional Lab., Peoria,111., June 1952, p. 3.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,2,857,367 October 21, 1958 James J Kearney It is hereby certified thaterror appears in the printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 49; for "disadvantage" read disadvantages column 5, line2, for "diffierent" read different column 9,

lines 1 and 2, for "monomer" read monomeric mixture Signed and sealedthis 10th dayvof February 1959.

(SEAL) Attest:

KARL H, AXLINE ROBERT C. WATSON Attesting Oflicer Commissioner ofPatents

1. THE PROCESS OF PRODUCING HIGH-QUALITY POLYMERIC MATERIAL WHICHCOMPRISES DISPERSING A POLYMERIZABLE MONOETHYLENIC MONOMER IN WATER WITHTHE AID OF DEXTRAN IN AN AMOUNT WITHIN THE RANGE FROM ABOUT 0.025% TO1.0% BY WEIGHT OF THE MONOMER AND EFFECTING POLYMERIZATION OF SAIDMONOMER WHILE SO SUSPENDED.